Enhanced visual selection after 2 mA cathodal tDCS of right intraparietal sulcus in healthy subjects

Selective visual attention, i. e. the ability to focus on relevant while ignoring irrelevant information in a crowded surrounding is an essential capacity of the human brain for everyday living. Previous studies suggest that the parietal cortex–and in particular the right intraparietal sulcus (rIPS)–is a key region for endogenous control of selective visual attention (i. e. top-down control) and spatial distribution of attention across both visual hemifields. In the present study, cathodal transcranial direct current stimulation (tDCS), a non-invasive brain stimulation technique, was used to modulate rIPS function in twenty healthy volunteers. As there is evidence that different current strengths influence cortical excitability distinctly (Nitsche et al., 2008), we investigated the impact of 1 mA and 2 mA cathodal tDCS on selective visual attention. After cathodal tDCS of the rIPS with 1 mA (current density: 0.0286 mA / cm²), 2 mA (0.0571 mA / cm²) or sham stimulation, subjects were asked to detect and verbally report predefined target letters, while ignoring irrelevant distractor letters. This partial report task is based on the theory of visual attention (Bundesen, 1990), which describes a computational framework to investigate different parameters of attentional processing: top-down control and attentional weighting. Only cathodal 2 mA stimulation effects on visual processing: Top-down control was significantly increased across hemifields. The attentional weighting was not affected by cathodal tDCS. Our findings strongly support the role of the rIPS as a key structure for selective visual attentional processing in both visual hemifield. Further, the data stress the importance of using the appropriate current strength in tDCS protocols.